Why did trichotillomania evolve in humans?

Recently I read a chapter from a book about how depression could have been advantageous 150,000 years ago because it provided a human with rest to recuperate while also withdrawing from the tribe to prevent disease spread within. Could trichotillomania have been an advantage 150,000 years ago too? If so, what was the advantage?

150,000 years ago humans lived in tribes and life expectancy was in the 20’s. Many women died in childbirth and many men died hunting and fighting. Still natural selection occured to pass down traits we still have today.

If you did live in a tribe, you presumably shared things or were in close quarters …..like caves.

A millennial human photographing humble beginnings and then hashtagging “woke”.

A millennial human photographing humble beginnings and then hashtagging “woke”.

I keep thinking what would happen if you woke up infested with lice or mites or some of the sort. It would be an issue to have hair. Lice would cause itching and sleep loss. Sleep loss would put you at risk for not reacting quickly to lethal threats. Not to mention lots of scratching could lead to infection which without medical treatment could eventually lead to further issues. Head lice have been around for a long time.

Genetic studies suggest that lice developed about 1.68 million years before homo sapiens emerged, and that they started their relationships with humans about the same time human evolution separated from chimpanzee evolution.

Could obsessive hair removal been an evolutionary advantage then? Lice was probably common and bald patches would have limited the area lice could thrive. No hair = no lice.

Having no eyelashes would have been one of the only ways to get rid of lice living on your lashes 150,000 years ago. Think about that for a second…….lice can happily live on your lashes!

Perhaps, this "urge" or "itch" we feel to pull, is an old physiological response to pre-emptively protect us from a possible lice infestation in our eyes and scalp. Perhaps this trigger is stress related since meeting new tribes or moving locations would have been stressful which are also common ways to get lice.

The problem is our genes don't evolve as quick as technology. While hair pulling could be useful then, it does not serve as much of a purpose now (assuming it did at all).

Millennial humans reach more tribes than their ancestors with the advent of social media.

Millennial humans reach more tribes than their ancestors with the advent of social media.


These are just thoughts of course but maybe if you are a hair puller, you are just born in the wrong century to appreciate it?

If you are wondering how mental disorders could have evolved in humans, check out this article from 2017 in Scientific american; https://www.scientificamerican.com/article/geneticists-are-starting-to-unravel-evolution-rsquo-s-role-in-mental-illness/

“Another team, lead by human geneticist Renato Polimanti at Yale University in New Haven, Connecticut, is trying to tease out links between environmental factors, mental illnesses and behavioural traits. Polimanti and his colleagues looked at 2,455 DNA samples from individuals at 23 sites across Europe and quantified each person’s overall genetic risk for mental disorders, such as autism, and personality traits, such as extraversion. They then calculated whether that risk was associated with certain environmental factors, such as rainfall, winter temperatures or the prevalence of infectious disease—exploring the idea that these factors might have been involved in selecting for the human traits.

People who live in European regions with relatively lower winter temperatures, they found, were slightly more genetically prone to schizophrenia. Polimanti suggests that if genes that helped people tolerate cold were located close to variants that promote schizophrenia in the genome, then the latter could have been inadvertently carried along during evolution as a “fellow traveller”.

Emily Kight